MEMs (Microelectromechanical system) devices usually cannot provide fully differential structures. For example, in an approach, when a MEMs accelerometer is used with a C-V converter (e.g., a capacitor-to-voltage converter) that requires a fully-differential signal, a modulating signal is applied at the single proof mass of the MEMs device and the differential inputs of the C-V converters are coupled to the other two electrodes of the same MEMs device. The large modulating signal, however, generally creates a large common mode signal coupling to the inputs, which cannot be easily suppressed, and, as a result, can cause corruption at the output. To really suppress this large common mode signal, an input common mode feed back is required, which makes the accelerometer more complicated.
Another approach related to MEMs accelerometer type I uses a differential amplifier to feedback a reverse signal and drive a pair of capacitors. To completely suppress the input common mode signal, the same reverse signal and the same capacitor values are required but difficult to fabricate, and create extra loading affecting circuit bandwidth. Further, capacitor mismatch, if it exists, can create a differential signal that may corrupt the MEMs signals. Additionally, extra circuitry may be required to maintain the DC input common mode level.
Another approach related to MEMs accelerometer type II does not provide full-differential signals for inputs, causing the charge injection to offset the signals. To solve the problem a reset signal and complex clock scheme is needed.
A capacitive-amplifier approach using feedback resistors to set input common mode requires very large resistance, commonly implemented by MOS transistors. The resistor, however, cannot sustain the common voltage due to device leakage when the resistance is large.
Like reference symbols in the various drawings indicate like elements.